2. analog
  3. 187888-174921

Vibration Question

Warning to the sensitive: involves tonearm pods.

I know this topic is beyond the pale to some, but my tables cannot take a second tonearm (once upon a time, though, they did), and I enjoy variety in cartridges. I have bought four pods so far from Lee Drage at Acoustand, two plain and two with built in micrometer VTA adjustment. But I discover the airspace around the tables is too congested with six arms, as well as introducing some grounding issues. So, as I told pindac the other day, I started to experiment with using two pods per tonearm. Not just a simple 'if one is good then two must be better' but for practical reasons. Firstly, a pod resting on three spikes weighs about 10lb, but it doesn't take much pressure on the distal end of the arm panel to cause it to tip. One can spoil a carefully set up alignment that way, and if it continues tipping a disaster could happen. So, I thought, why not place a pod under the distal end of the tonearm panel, and prevent that happening?

But then a second thought came along: if the second pod were firmly coupled to the panel, I would double mass and damp vibrations even more. That's a bit theoretical to me, as my oak chest weighs ~350lb and I can stamp on the floor next to it and not disturb a playing stylus. But rigidity is rigidity. So I asked Lee if he could make me a double ended panel with an SME mount centred in the middle. Roughly, like this:

He agreed, and pointed out I would have to forego the VTA adjustment, unless one were to place a screw at each end! I can use the SME mount itself to adjust VTA. though, so that's OK.

Here, finally is the question: he thinks I am simply introducing twice as many vibrations (external, I think he means) into the tonearm by having it rest in two sites on the oak chest, and that I would be better off having one end of the tonearm panel free-floating. My view is that rigidity is paramount, and if a built-in tonearm on a table is firmly coupled to the table then I am moving a bit closer to that ideal by having a firmly coupled chest-table-pod system. What say you?

dogberry
dogberry OP
580 posts
 

Well, the 18th century oak chest wins over all other considerations! It's worth more than all my hi-fi and records.

fsonicsmith's avatar
fsonicsmith
938 posts
 

Well, the 18th century oak chest wins over all other considerations! It's worth more than all my hi-fi and records.

Don't take me literally. I meant to ditch it as the base for your turntable. Looking at the photo you posted the chance of the two pods being in the same plane as the platter surface when seated on different planks making up the top of the chest is quite small. If the shaft of the tonearm is not "laying" in the same plane as the top of the platter then you are stymied before you begin to worry about the other aspects such as excessive vibration. 

dogberry OP
580 posts
 

But a spirit level says the tonearm panel is level. That's surely the best I can hope for, no?

fsonicsmith's avatar
fsonicsmith
938 posts
 

You asked for help. The rest of are not there and can only go off of the available information. I gave you my very best guess and very questionable opinion. 

mijostyn's avatar
mijostyn
8,251 posts
 

@fsonicsmith 

Well, go figure.

@dogberry 

I think you are looking at it from the wrong direction. Three points describes a plane. Four feet rock. When it comes to mechanical devices simplicity is almost always best. The fewer pieces you have the fewer resonances and interactions you have to control.   Ideally you would have one critically damped non resonant chassis to which the tonearm and platter bearing are securely bolted. The Basis Inspiration is an example of such a turntable. The problem with this design is that it can get messy if one wants to switch tonearms. Turntables like the Linn LP12 and the Sota Sapphire use removable tonearm boards which can be drilled for each arm. In the case of the Sota Cosmos the board is a 1" thick constrained layer construct of acrylic and aluminum weighing several pounds. It and the tonearm are bolted firmly to a 1" thick aluminum chassis that has been drilled out in a pattern to reduce weight and control any resonance. In this case the spindle is mounted to the chassis and the whole affair is hanging by four dampened springs. 

Does any of this lead to a better sounding turntable? The honest answer is I have no idea. There are to many variables involved, the quality of the system, the quality of the listener, cartridge set up, tonearm matching and so forth. From a purely technical standpoint it is the right way to do things and I can't not believe that all these "right ways" do not add up. 

More to discover